E30 series BMW 3

since 1983-1994 of release

Repair and car operation

+ 1. Maintenance instruction
+ 2. Maintenance
+ 3. Engine
+ 4. Cooling system
+ 5. Heating and ventilation
+ 6. Fuel system
+ 7. Exhaust system
+ 8. Transmissions
+ 9. Coupling
+ 10. Brake system
+ 11. Running gear
+ 12. Body
+ 13. Electric equipment
- 14. Good advice
   14.2. Changed numbers
   14.3. Purchase of the old car or mysterious set of figures and letters
   14.4. Durability of the car
   14.5. About parallelism of bridges of the car and the trailer
   14.6. Preparation of the car for winter
   14.7. Rule 35
   14.8. Choice of the second-hand car
   14.9. Engine oils
   14.10. That it is necessary to know, changing oil
   14.11. Emergence in deposit oil
   14.12 whether. It is possible to mix import oils?
   14.13. "Eats" much, but silently goes
   14.14. It is rather live, than it is dead …
   14.15. It is not got - good advice
   14.16. Visit to car-care center
   14.17. A gear belt for a drive of the mechanism of a gazoraspredeleniye
   14.18. Wear of pistons
   14.19. Valves
   14.20. Bearings of engines
   14.21. Engine pollution
   14.22. As the conditioner works and what to do, if it failed
   14.23. Conditioner: not only "pluses", but also "minuses"
   14.24. Rules of service of the conditioner
   14.25. It is not necessary to stir antifreeze with antifreeze …
   14.26. That it is necessary to know upon purchase of the air filter
   14.27. Engine overheat
   14.28. That it is necessary to know to the owner of the car with the injector engine
   14.29. Accumulator
   14.30. Possible malfunctions of the storage battery
   14.31. What to do with the failed generator
   14.32. The belt is guilty, and we blame the generator
   14.33. Catalyst
   14.34. Rub in one - or how to save the catalyst
   14.35. Probuksovochka
   14.36. Features of operation of brake system
   14.37. Malfunctions of brake system
   14.38. Brake liquids
   14.39. ABS: natural choice
   14.40. Rims
   14.41. We update rims
   14.42. Scheme of marking of a car tire
   14.43. Metal corrosion
   14.44. Automake-up
   14.45. What creaks?
   14.46. Hatch
   14.47. Safety cushion: troubles or pleasures?
   14.48. We fit well?
   14.49. Anticreeping "immunodeficiency"
   14.50. Why headlights grow dull
   14.51. "Galogenki"
   14.52. About the correct adjustment of headlights
   14.53. Electric motor
   14.54. From change of places "composed" changes nothing?


14.36. Features of operation of brake system


Skilled motorists know that in the rainy summer the brake system of the car for some reason becomes more whimsical, than, for example, in a heat. Troubles can directly begin in тараже. You came early in the morning to the car, sat down at a wheel and only touched a brake pedal, – as it, darling, powerlessly failed to the floor. Also that annoyingly – after all still yesterday the pedal was habitually rigid. However, the free wheeling was more usual, but you, possibly, did not give it value. And in vain... Now in the upset feelings you leave the car and look under it. Indeed: on the back party of one of basic boards of back wheels and on a brake drum extensive smudges of brake liquid. Having opened then a cowl and having glanced in a reserve tank with brake liquid, are convinced that almost all it flowed out. Affairs are bad. About a trip cannot be and speeches. Repair is necessary. But because of what such occurred? And why so suddenly?

Well, first, not too suddenly. Most likely, you simply did not notice the podtekaniye beginning earlier. And secondly, let's understand the reasons of such refusal of a brake drive, unfortunately, characteristic for cars of respectable age.

Let's remember bases of a design of a modern hydraulic drive of brake mechanisms. It turns on the main brake cylinder with a reserve tank for brake liquid, the vacuum amplifier, a double-circuit regulator of pressure in back brake mechanisms and a brake pedal. The hydraulic drive of brake mechanisms is divided into two independent contours. One contour ensures functioning right forward and left back of wheels, another – left forward and right back. Such diagonal scheme of division of contours is widespread today in cars of leading world firms. It considerably increases traffic safety in comparison with earlier applied schemes.


Pressure of liquid in pipelines and wheel brake cylinders at intensive braking can reach 10–12 MPas (100–120 kg/cm2). Therefore consolidation of all pipelines, and furthermore, mobile parts of a drive – the major requirement to a design. And if motionless connections of pipelines to pressurize rather easily, mobile parts – pistons of the main brake cylinder, wheel cylinders and the amplifier – more difficult to condense.

The world practice of producers of cars knows today two types of rubber sealants of cuffs: continuous, chasheobrazny, without the central opening and in the form of rubber washers with a convex external surface. The first are applied today seldom, the second – are most widespread, as cheaper and technological.

Design and principle of work of such consolidation we will consider on an example of a typical design of the main brake cylinder of tandemny type. In its case two mobile pistons creating two independent contours of a brake drive are placed. Tightness of a back part of the piston is provided to rubber cuffs. However this of cuffs will not prevent a liquid effluence outside if the main consolidation – cuffs – wore out. It is rather the boot protecting the piston from dirt from outer side. The main consolidation of pistons – cuffs. Prior to the beginning of braking pistons are motionless, and cuffs do not adjoin to their face surfaces as are kept by the rasporny rings resting against adjusting bolts. At such position of pistons of a cavity of the cylinder are filled with the brake liquid passing from a reserve tank through gaps between cuffs and the piston. The main cuffs have section of a toroidal form. Their external diameter in a free condition slightly exceeds internal diameter of the brake cylinder. Therefore, if cuffs is not exposed to pressure of brake liquid, only its average external corbel adjoins to a cylinder mirror. For this reason at the slightest wear of outer side a cuff – let it will be all unique risk – liquid will start to follow outside. And it, notice, when parking car.

By pressing a brake pedal the piston moves forward and the cuff contacts with a face surface. Reliability of contact is provided with a spring. From this point the message of an internal cavity with a reserve tank stops, and pressure and in pipelines starts to increase in the cylinder. Under the influence of this pressure of liquid of cuffs it is distributed in the radial direction and reliably nestles on a mirror of the cylinder all external surface.

The second, floating, the piston of the main brake cylinder moves under the pressure of liquid, and work its cuff differs nothing from the described. Also cuffs of wheel brake cylinders in the same way work. Because in intervals between braking the area of contact of cuffs with cylinders is minimum, good greasing of surfaces of the cylinder is provided with brake liquid. Besides, the beginning of braking occurs smoothly, without breakthroughs that essentially improves comfortableness and traffic safety of the car.


The cavities which are forming between details of the main brake cylinder in intervals between braking, have the volume which is completely providing compensation of thermal expansion of brake liquid at repeated or long braking, excepting thereby self-jamming of brake mechanisms. Besides, free circulation of liquid at warming up and the subsequent cooling of system reduces probability of a contamination of cylinders dirt, and also facilitates spontaneous removal of vials of air from the main brake cylinder (from wheel cylinders air, unfortunately, by itself will not be removed – system pumping is necessary).

So to undertake, if brakes began to flow? Let's begin with the most widespread – from repair of wheel brake mechanisms. Cylinders of back drum-type brake mechanisms flow more often than lobbies disk (for the disk jamming of pistons, instead of course of cuffs is characteristic). We offer sequence of the actions, which performance quite under force to any driver and does not demand any special adaptations.

First of all it is necessary to weaken bolts or nuts of fastening of wheels, and then, having lifted the car a jack and having substituted under it a safety support, to remove a wheel. Further it is necessary to remove a brake drum. On many cars it more is not fixed by anything and after wheel dismantle easily acts in film manually. In case of fastening, except wheel bolts also directing screws removal of a drum makes a certain difficulty. Often after untwisting of these screws the drum does not manage to be removed from an aligning landing corbel of a semi-axis. Especially if he after factory assembly never acted in film and as speak, became attached.

It is necessary, of course, to try to twirl the removed directing screws in special carving openings, operating with them, as a stripper. However often it conducts only to carving breaking, and the drum – will not stir. Then resort to the following operation. Having reliably fixed linings wheels standing on the earth, start the engine, include a low gear and at drum rotation with small speed sharply press a brake pedal. In case the hydraulic drive does not work, sharply brake the parking brake. As a rule, at such dynamic loading the semi-axis is turned in a drum opening then to remove a drum any more does not make work.

After removal of a drum weaken a cable of the parking brake and remove its tip from the lever. Having taken out from a finger opening шплинт, remove the lever (on some models of cars removal of this lever not obligatory). Further release from a basic board brake shoes, having removed directing springs, and start removal of blocks. A widespread mistake thus is attempt to remove first of all the top spring which is pulling together blocks. To make it it is very difficult, especially barehanded or with only one screw-driver. Where it is simpler to remove at first the bottom, weaker spring, then to put forward the bottom ends of blocks from grooves of a support and, having displaced a little block on itself and operating with them as long levers, to stretch the top spring and to remove a raszhimny level of the parking brake, and then and blocks from basic cuts of pistons of the brake cylinder. It is very important not to damage rubber protective caps of the cylinder thus.

Now it is possible to disassemble the wheel brake cylinder. Here it would be desirable to give such advice. If it is not a pity to you old brake liquid, it is possible to remove at once protective caps and by means of a drift from a soft material выпрессовать from the cylinder pistons assembled with details of automatic control of a gap. Liquid thus will pour out on the earth. If liquid has to be kept, better to disconnect a tube from the wheel cylinder and to muffle it a wooden stopper. After that the cylinder remove from a basic board and continue its dismantling on a workbench. By means of a screw-driver turn the piston, unscrew from it the persistent screw and remove cuffs with a basic cup and crackers. Then separate a persistent ring and the screw.

After dismantling all details wipe and attentively examine a surface of the cylinder and cuffs. The mirror of the cylinder should be absolutely pure and smooth, without рисок and roughnesses, and on an external surface of cuffs should not be even the slightest roughnesses.


On a mirror of the cylinder it is possible to eliminate minor defects with grinding in, considering thus that the increase in its diameter is very undesirable. Cuffs should be changed on new even if the old have no visible wear. It is necessary to check also, whether protective rubber caps of the cylinder are damaged and if necessary to replace them new.

Before assembly it is necessary to grease plentifully all details with brake liquid and to execute the specified operations upside-down. After assembly it is necessary to check moving of pistons in the cylinder, having compressed pistons hands. They should move without breakthroughs and jammings.

The general assembly of the brake mechanism carry out to sequences, the return specified.

The last that it is necessary to make is to fill a brake drive with liquid and to remove from it air. For this purpose fill a reserve tank with fresh brake liquid to a label "MOVE". Then start air removal from the wheel cylinder of the most remote wheel. For this purpose put on an union head a rubber hose, and its free end lower in the transparent vessel which has been partially filled with brake liquid. Having sharply pressed a pedal of a brake of 3-5 times with an interval in 2–3 with, unscrew the union on a half-turn, continuing pressing a pedal (two persons are for this purpose necessary). Air with brake liquid will leave a tube. Further, lowering pedals, wrap the union. Repeat all operation until the tube will not cease to leave air vials, the pedal does not become "rigid". The same operations repeat for other wheels of the car.

It is necessary to notice that pumping of system can be executed and to one. For this purpose it is necessary to execute all specified preparatory operations. However after untwisting of the union it is necessary most to sit down at a wheel and to press a pedal of a brake 3–4 times. Then, without removing a tube and without taking out it from liquid in a vessel, to wrap the union to the full. Then again to sit down at a wheel and to check "rigidity" of a pedal. If its course though decreased a little, to start the same operations serially with other wheels of the car. When pumping the last brake cylinder the pedal should be the most rigid, and its course – more than 1/2 a full speed. At removal of air it is absolutely necessary to watch эа decrease in level of liquid in a reserve tank and constantly to add it. Certainly, alone described operations on pumping of a brake drive will take more time, than together. However then you are once again convinced what to cope with this type of repair it is possible quite independently.